* configure.in: Convert to autoconf 2.57, gratuitous stylistic

	cleanup, rename to configure.ac.
	* configure.ac: Renamed from configure.in.
	* config.h.in: Rebuilt with autoheader 2.57.
	* configure: Rebuilt with autoconf 2.57
	* README: Update to reflect rename of configure.in to configure.ac.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@78668 138bc75d-0d04-0410-961f-82ee72b054a4